Preparation of GREEN Anion Exchangers for the Decolourisation of Sugar Processing Solutions

The cane and beet sugar refining process is mainly focused on removing coloured compounds which alter the quality of the final product. Traditionally, the refining process includes affination which removes 35-55 % of coloured impurities, carbonatation or phosphatation which eliminates 40-60% of the remaining colour, and decolourisation by active carbon, bone char or ion exchange to complete the process. The ion exchange resin process is currently considered as one of the most efficient sugar liquor decolourisers. High molecular weight sugar liquor colourants such as melanines, melanoidines, caramels, and polyphenols can be adsorbed onto the resins. Regeneration of the resin is by desorption with alkaline solution. In the current experiments, sugar cane bagasse, waxy starch and wheat straw were crosslinked with epichlorohydrin in presence of NaOH, NH4OH or imidazole. The resultant waterinsoluble products were characterized by anion-exchange capacity, packed volume, and colour-binding properties. The rate of decolourisation was measured by the conventional ICUMSA method: The sample was diluted to 5 brix, adjusted to pH 7.0 and filtered. The optical density was measured at 420 nm using a spectrophotometer. Yields were highest using 2.5-3:1 epichlorohydrin to NH4OH molar ratio, producing weak anion exchangers with moderate dye-binding capacities in all cases. A 2.5:1 epichlorohydrin to imidazole molar ratio proved best for enhanced anion exchange capacities especially for bagasse and waxy starch combination. The dye-binding capacities were comparable to the commercial synthetic ion exchange resin such as LEWATIT S 6328 A.